Investigations are focusing on the hormonal regulation of male sex accessory organ epithelium & fibromuscular stroma. Based primarily on analyses of 3H-hormone localization and hormone receptor concentrations, it is hypothesized that sex accessory organ stroma function can be enhanced by estrogen as well as androgen. Androgens are the prime regulator of epithelium function. Studies involving treatment of castrate animals with estrogen and non-aromatizable androgens support these ideas, and current and future effort is directed toward (1) elucidating the principal endogenous hormonal agonist of the stroma and (2) developing effective and selective inhibitors of sex accessory organ epithelium and stroma.